LOWER SILURIAN. 163 



SUBDIVISIONS OF THE SILURIAN. 

 A. LOWER SILURIAN. 

 I. Primordial or Cambrian Period (2). 



1. Acadian Epoch (2 a). Shale and sandstone at St. John, 

 New Brunswick, the St. John group of Matthew and Logan, the 

 Acadian group of Dawson ; beds at St. Johns and elsewhere, in 

 Newfoundland ; clay-slate and siliceous slate of Braintree, Mass. ; 

 Ocoee conglomerate and slates of East Tennessee and North 

 Carolina. 



2. Potsdam Epoch (2 5). Sandstone of Potsdam and other 



places in northern and northeastern New York, western Vermont 



and Canada ; sandstone and limestone of Troy, N. Y. ; slate and 



limestone of northwestern Vermont, including the Georgia shales ; 



limestone and sandstone of shores of the Straits of Belle Isle ; 



Chilhowee sandstone of East Tennessee ; sandstone with some 



limestone in Wisconsin and Minnesota. 



In Great Britain, the Cambrian, including beds in the Longmynd, in North 

 "Wales, the Harlech beds in Pembrokeshire, and the overlying Menevian beds, 

 and also, higher in the series but conformable, the Lingula flags. In Bohemia, 

 Barrande's Stage C, and perhaps his B, or part of it. In Sweden, Angelin's A 

 and B, the Alum slate and Fucoidal sandstone. 



II. Canadian Period (3). 



1. Calciperous Epoch (3 a). Calciferous sandrock in New 

 York. Lower Magnesian limestone of the Mississippi valley ; St. 

 Peters sandstone of Wisconsin and Illinois ; Knox sandstone, 

 East Tennessee ; thick limestones (part of the so called Quebec 

 group) of Newfoundland. 



2. Quebec Epoch (3 b). Levis formation, Canada, near Que- 

 bec ; Taconic slates of Green Mountains ; shales, limestones, and 

 sandstones, Newfoundland. Part of the Knox group, Tennessee. 



3. Chazy Epoch (3 c). Chazy limestone of New York, Can- 

 ada, etc. Part of the crystalline limestone of the Green Moun- 

 tains in Vermont and to the south. 



Tremadoc slates of North Wales; Skiddaw slates of northern England; Arenig 

 or Stiper stones group (the Lower Llandeilo of Murchison). Angelin's group 

 B C in Sweden. The Pleta of Russia, according to Billings, and the Ungulite 

 grit of Pander. 



III. Trenton Period (4). 



1. Trenton Epoch (4 a) : (1) Birdseye limestone, (2) Black 

 River limestone, (3) Trenton limestone ; Galena limestone of Illi- 

 nois, etc. ; Lebanon limestone of Middle Tennessee. 



In Great Britain, Llandeilo group. In Bohemia, Barrande's formation D'. In 

 Sweden, Angelin's C, Orilioceratite limestone. v -• ' ; ' ' ' 



